Conventionally, transparent epoxy resin compositions have been widely used for encapsulating optical semiconductor elements such as LEDs. These epoxy resin compositions typically comprise an alicyclic epoxy resin, a curing agent and a curing catalyst, and are used in a molding method such as a casting or transfer molding method, by pouring the composition into a mold having an optical semiconductor element positioned therein and subsequently curing the composition, thereby encapsulating the optical semiconductor element (see Patent Document 1).
However in recent years, as the brightness and output of LEDs have continued to increase, problems have started to emerge for conventional transparent epoxy resin cured products, including discoloration of the resin over time upon exposure to short wavelength blue light or ultraviolet light, and the occurrence of cracking during temperature cycle tests.
Known techniques for preventing this type of light degradation include introducing epoxy groups and/or oxetanyl groups into a siloxane (see Patent Document 2), and introducing epoxy groups into a silsesquioxane (see Patent Document 3).
Furthermore, the use of a hard rubber-like silicone resin as a protective coating for preventing cracking has also been proposed (see Patent Document 4). Moreover, the use of a silicone resin containing introduced isocyanuric acid derivative groups as a stress reduction agent for an epoxy resin cured product is also known (see Patent Document 5).
However, if the above compositions are used within case-type light emitting semiconductor devices, namely devices in which a light emitting element is placed inside a ceramic and/or plastic casing, and the inside of the casing is then filled with the silicone resin, then none of the compositions is able to provide totally satisfactory levels of both light resistance and crack resistance.
[Patent Document 1] JP 7-274571A
[Patent Document 2] JP 2004-238589A
[Patent Document 3] JP 2005-263869A
[Patent Document 4] US2002/0190262A1
[Patent Document 5] JP 2004-99751A